# Copolymerization

 Subject classification: this is a chemistry resource.

## Aims

• Copolymer composition

## Introduction

• Polymerization of two or more monomers
• Properties of the polymer depend on monomer composition and time

## Statistical copolymerization

 RM1• + M1 → RM1M1 rate=k11[RM1•][M1] RM1• + M2 → RM1M2 rate=k12[RM1•][M2] RM2• + M1 → RM2M1 rate=k21[RM2•][M1] RM2• + M2 → RM2M2 rate=k22[RM2•][M2]
• Monomers are consumed at different rates
• Therefore the polymer composition changes during the reaction

 Instantaneous copolymer equation ${\displaystyle F_{A}={\frac {r_{A}f_{A}^{2}+f_{A}f_{B}}{r_{A}f_{A}^{2}+2f_{A}f_{B}+r_{B}f_{B}^{2}}}}$  Defines the polymer composition at any moment in time. FA = amount of monomer A in the polymer. fA = amount of monomer A in the monomer feed. FA + FB = 1 fA + fB = 1

 Reactivity ratios ${\displaystyle r_{A}={\frac {k_{AA}}{k_{AB}}}}$  and ${\displaystyle r_{B}={\frac {k_{BB}}{k_{BA}}}}$  Defines the relative rates of reaction. Ratios are set for any pair of monomers. No variation with solvent, concentration, temperature, etc. rA > 1 → HOMO propagation preferred rA < 1 → CROSS propagation preferred